Field
The present specification generally relates to glass compositions and, more specifically, to glass compositions which have a relatively low average CTE and which are amenable to strengthening by ion-exchange and glass articles comprising the same.
Technical Background
Glass articles, such as cover glasses, glass backplanes and the like, are employed in both consumer and commercial electronic devices such as LCD and LED displays, computer monitors, automated teller machines (ATMs) and the like. Some of these glass articles may include “touch” functionality which necessitates that the glass article be contacted by various objects including a user's fingers and/or stylus devices and, as such, the glass must be sufficiently robust to endure regular contact without damage. Moreover, such glass articles may also be incorporated in portable electronic devices, such as mobile telephones, personal media players, and tablet computers. The glass articles incorporated in these devices may be susceptible to damage during transport and/or use of the associated device. Accordingly, glass articles used in electronic devices may require enhanced strength to be able to withstand not only routine “touch” contact from actual use, but also incidental contact and impacts which may occur when the device is being transported.
Various processes may be used to strengthen glass articles, including chemical tempering, thermal tempering, and lamination. Chemical tempering generally involves exchanging smaller alkali ions in the glass article (such as lithium ions and/or sodium ions) for larger alkali ions (such as potassium ions) by submerging the glass article in a molten salt bath which contains the larger alkali ions. Accordingly, in order to facilitate the chemical tempering or ion-exchange process, the glass article generally includes a relatively high concentration of alkali ions.
The presence of alkali ions in the glass article generally increases the average coefficient of thermal expansion of the glass article and, as such, the glass article may not be suitable for use in applications where a glass article with a relatively lower average coefficient of thermal expansion is required, such as the clad glass of a laminate strengthened glass article.
Accordingly, a need exists for alternative glass compositions which have a relatively low average coefficient of thermal expansion and which are also amenable to strengthening by ion-exchange, and glass articles incorporating the same.